The IEEE (Institute of Electrical and Electronic Engineers) 802.16WG (Working Group) has proposed a point-to-multipoint (P-MP) communication system wherein a plurality of mobile stations (MSs) can be connected to a base station (BS). For example, a concept of a communication system according to the 802.16d and 802.16e standards is illustrated in FIG. 1 as an example of a P-MP communication system.
FIG. 2 is an example of the frame structure according to 802.16d/e, illustrating a DL (downlink) sub-frame and a UL (uplink) sub-frame.
In FIG. 2, the preamble signal (“Preamble”) at the start of the DL sub-frame is a synchronization signal sent from a base station to mobile stations, and the mobile stations synchronize with the base station in response to receiving this preamble signal.
The “DL-MAP” and “UL-MAP” contain information on the frame structures, control information, and the like for the DL and UL sub-frames, respectively. The mobile stations perform DL reception processing and UL transmission processing by making reference to the DL-MAP and the UL-MAP, respectively.
The “CDMA (Code Division Multiple Access) Contention Region” defined in the UL sub-frame is a region used for sending a Ranging Code for adjusting a transmission power and timing at a mobile station, and a Bandwidth Request Code for requesting allocation of a UL communication region for sending a bandwidth request, from a mobile station to a base station.
Such a CDMA Contention Region is a contention region in which any mobile station can send a CDMA code, without being specified by a base station. In preparation for sending a CDMA code, each mobile station selects a slot from this CDMA Contention Region on which the CDMA code is to be sent.
In this particular example, there are 256 patterns of CDMA codes, and the ranges of the patterns are defined depending on information to be sent. For example, if a mobile station sends a CDMA code for a bandwidth request, the mobile station selects one CDMA code from the CDMA code pattern ranges for bandwidth requests, and sends the selected one to the base station.
FIG. 3 illustrates one example of a UL MAP information element (IE) broadcasted to mobile stations when a base station sets a CDMA Contention Region to a UL sub-frame.
In FIG. 3, the “CID (ConnectionIdentifier)” is an identifier for a connection, which is set by the base station for all mobile stations for broadcasting.
The “UIUC (Uplink Interval Usage code)” indicates the type of the UL MAP IE, using which the type of UL MAP IE can be identifiable. For example, the value “12” is set for the CDMA Contention Region.
In addition, the location of the CDMA Contention Region within the UL sub-frame is specified in the “OFDMA Symbol offset”, “Subchannel offset”, “No. OFDMA Symbols”, and “No. Subchannels”, and the purpose of the CDMA Contention Region is specified in the “Ranging Method”.
For example, the purposes of a CDMA Contention Region that can be specified in “Ranging Method” include Initial Ranging, Handover Ranging, Periodic Ranging, and Bandwidth Request.
FIG. 4 depicts an example of the sequence when a mobile station requests allocation of a communication region to a base station.
In S1, the mobile station selects one CDMA code from pattern ranges divided for the purpose of Bandwidth Request, and sends the selected one to the base station.
In response to receiving the CDMA code from the mobile station in S1, in S2, the base station sends a CDMA allocation IE to the mobile station, thereby specifying a communication region in the UL sub-frame which the mobile station uses for sending a Bandwidth Request message. Since the base station does not know which mobile station has sent the CDMA code received by the base station, the base station also sends the location of the received CDMA code in the CDMA Contention Region and information on that code pattern.
In S3, the mobile station sends a Bandwidth Request message to the base station in the communication region in the UL sub-frame specified in the CDMA Allocation IE received from the base station in S2. The Bandwidth Request message contains information on the data size of the data the mobile station intends to send.
In S4, the base station allocates a communication region in the UL sub-frame, based on the data size specified in the Bandwidth Request message received from the mobile station in S3, and specifies it in a UL-MAP.
In S5, the mobile station sends data in the communication region in the UL sub-frame specified in the UL-MAP received from the base station in S4.
An example of a UL-MAP IE containing a CDMA allocation IE which is sent from the base station to the mobile station in FIG. 4 is illustrated in FIG. 5.
In FIG. 5, the “Duration” specifies the number of slot(s) allocated to the mobile station by the base station.
The “UIUC” specifies the Burst Profile which is information on modulation and coding used for sending a Bandwidth Request message and the like, in the communication region specified in the CDMA allocation IE.
The “RepetitionCodingInformation” specifies information on the Repetition Code.
The“FrameNumberIndex”, “RangingCode”, “RangingSymbol”, and “Ranging Subchannel” specify information on the CDMA code received by the base station. The mobile station which has sent the CDMA code having the pattern indicated in the “Ranging Code” at the location of the “Ranging Symbol” and “Ranging Subchannel” in the frame indicated by the “Frame Number Index” can be identified.
The “Bandwidth Request Mandatory” specifies whether sending a Bandwidth Request message is mandatory or not.
As described above, if a mobile station sends a CDMA code in the CDMA Contention Region, the base station does not know which mobile station has send the CDMA code from that code received by base station. The base station thus specifies the mobile station which has send the CDMA code by including information on the received CDMA code and the location information within the frame in a CDMA allocation IE and sends the CDMA allocation IE. In response to receiving the CDMA allocation IE, the mobile station sends a message to the base station using a communication region in the UL sub-frame specified in the received CDMA allocation IE.
The 802.16m standard, which is the next version of 802.16e, is expected to be able to support not only mobile stations compliant with 802.16m (hereinafter referred to as “802.16m-compliant mobile stations”), but mobile stations compliant with 802.16e (hereinafter referred to as “802.16e-compliant mobile stations”).
An example of an 802.16m frame structure supporting both 802.16e-compliant and 802.16m-compliant mobile stations is illustrated in FIG. 6.
As depicted in FIG. 6, the 802.16m frame includes a region for communications between abase station and 802.16e-compliant mobile stations (hereinafter, referred to as an “802.16e communication region”) and a region for communications between the base station and 802.16m-compliant mobile stations (hereinafter, referred to as an “802.16m communication region”). Such 802.16m-compliant mobile stations are also capable of operating as 802.16e-compliant mobile stations, and making communications in the communication region for 802.16e-compliant mobile stations.
In the meantime, the WiMAX (Worldwide interoperability for Microwave Access) Forum has proposed the Fractional Frequency Reuse (FFR), as one use of frequency bands in a wireless communication system based on the 802.16 standards.
An example of the wireless frame structure used in an FFR-implementing communication system is illustrated in FIG. 7.
In FIG. 7, two time domains, R1 Zone and R3 Zone, are defined in a frame allocated to base stations BS1-BS3.
In the R1 Zone, a common frequency band is allocated to base stations BS1-BS3, while different frequency bands are allocated for the respective base stations in the R3 Zone. For example, one or more of frequency bands f1-f3 is allocated to the BS1-BS3 in the R1 Zone (the same frequency band may be allocated to the adjacent base stations), and different frequency bands are allocated in the R3 Zone, e.g., f1 is allocated to the BS1, and f2 to the BS2.
Here, it is assumed that the R1 Zone is allocated to a mobile station having a relatively better wireless quality with the base station, e.g., a mobile station located in the vicinity of the base station, while the R3 Zone is allocated to a mobile station having a relatively poor wireless quality with the base station, e.g., a mobile station located in the edge of the communication area serviced by the base station. In such a case, improved throughput and better coverage can be both assured.
As described above, in an 802.16m system and an FFR-implementing system, multiple communication regions are present in a certain frame, and a mobile station communicates with a base station in a communication region that is suited in view of the wireless specification, the wireless conditions and the performance of that mobile station, and the like.
Non-patent Document 1: IEEE Std 802.16TM-2004 Non-patent Document 2: IEEE Std 802.16eTM-2005 Non-patent Document 3: IEEE 802.16m System Requirements Non-patent Document 4: Mobile WiMAX—Part I: A Technical Overview and Performance Evaluation (August, 2006)
Even in the case of an 802.16m system and an FFR-implementing system as described previously, for example, a mobile station has to send a CDMA code to a base station for requesting allocation of a communication region to be used for sending a Bandwidth Request message.
As described above, upon receiving the CDMA code, the base station may not be able to, however, know which mobile station sends that CDMA code.
Thus, in the 802.16m system, since the base station does not know whether the mobile station sending the CDMA code is an 802.16e-compliant mobile station or an 802.16m-compliant terminal, for example, the base station has to allocate an 802.16e communication region to the mobile station which can be used by both 802.16e-compliant and 802.16m-compliant mobile stations.
However, the requesting 802.16m-compliant mobile station can communicate in an 802.16m region, accordingly, allocation in this manner may consume more 802.16e communication region resources, making allocation inefficient.
In contrast, similarly in an FFR system, a base station does not know whether a mobile station sending a CDMA code is a mobile station communicating in a communication region in the R1 Zone or a mobile station communicating in a communication region in the R3 Zone.
Accordingly, the base station have to allocate a communication region in the R3 Zone which can be used by both mobile stations communicating in an R1 Zone and an R3 Zone. Allocation in this manner may also consume more R3 Zone resources since a communication region in the R3 Zone is allocated to a mobile station communicating in an R1 Zone, also making allocation inefficient.
Note that an 802.16m system and an FFR-implementing system are merely non-limiting examples of communication systems to which the present disclosure is applicable.